1, in direct proportion: when the ratio between two variables remains the same, these variables are in direct proportion. This means that if one variable increases, another variable will increase accordingly, and if one variable decreases, another variable will decrease accordingly. The positive proportional relationship between two variables can be expressed by the following formula: y = kx (where y and x are two variables and k is a constant, called proportional constant).
2. Inverse proportion: When the product of two variables is constant, these variables are inverse proportion. This means that if one variable increases, another variable will decrease accordingly, and if one variable decreases, another variable will increase accordingly. The inverse relationship between two variables can be expressed by the following formula: y = k/x (where y and x are two variables, k is a constant, called a proportional constant, and x is not equal to 0).
Positive proportion and inverse proportion are widely used. For example, in engineering, they are used to calculate the relationship between various physical quantities, such as voltage and current, force and acceleration. In business, they are used to calculate the relationship between cost and output. For example, if the number of products produced by a factory increases, how will the cost change? In life, they are used to calculate the relationship between time, speed and distance, such as driving time or driving distance.